Characterization of Metastable Crystalline Forms in Ultrathin Polymer Films and Electrospun Polymer Nanofibers: Evolution, Revolution or Back-to-the-Future
Wednesday, March 10, 2021: 11:15 AM - 11:50 AM
Studies of rapid solvent evaporation in polymeric thin films and nanofibers fibers have revealed that metastable crystalline states can be induced and stabilized at high solvent evaporation rates. Electrospinning, a technique which relies on self-organization via electric charges and the interaction of the nanofibers with an applied field, is an efficient and versatile technique to produce ultrafine fibers with diameters down to the range of a few tens of nanometers. Due to the strong stretching forces and fast solvent evaporation kinetics associated with the electrospinning process, the resulting nanofibers can have a distinct crystallization behavior, compared to the bulk materials. This can lead to the formation of metastable phases or crystalline polymorphs. For some polymeric materials, more than one crystalline polymorph can be found in electrospun nanofibers and, correspondingly, in ultrathin films, and the population of each polymorph can often be controlled by varying the processing conditions. The implications of these observations are far reaching since the crystalline structure of a polymer plays an important role in its properties that are manifested after processing. Atomic force microscopy (AFM)/infrared (IR) spectroscopy (AFM-IR) and Resonance Photothermal IR (PTIR) Spectroscopy, based on the photothermal induced resonance effect, are powerful tools that provide spectroscopic and topographical information, which can be correlated with chemical, conformational and molecular orientation information at spatial resolutions of 50-100 nm (AFM-IR) and 500-5000 nm (PTIR). The latter is done in reflection and hence the polymeric material can be studied in its post-processed form. Examples of metastable crystalline forms in spider silk, Nylon 6, poly(1-butene) and poly(hydroxybutyrate) (PHB) random copolymers with hydroxyhexanoate (PHBHx) will be given.
Keywords: Please select up to 4 keywords ONLY:
Atomic Force Microscopy (AFM),Materials Characterization,Infrared Spectroscopy,Polymers